Recent seasonally adjusted and trend estimates are likely to be revised when original estimates for subsequent months become available. The approximate effect of possible scenarios on trend estimates are presented below. Generally, the greater the volatility of the original series, the larger the size of the revisions to trend estimates. Analysis of the building approval original series has shown that they can be revised substantially. As a result, some months can elapse before turning points in the trend series are reliably identified.

The graphs and tables which follow present the effect of two possible scenarios on the previous trend estimates: that the October seasonally adjusted estimate is higher than the September estimate by 2.6% for the number of private sector houses approved and 14% for private sector dwellings excluding houses approved; and that the October seasonally adjusted estimate is lower than the September estimate by 2.6% for the number of private sector houses approved and 14% for private sector dwellings excluding houses approved. These percentages represent the average absolute monthly percentage change for these series over the last ten years.